Lecture 20: The Basic Structure of the GI System Flashcards
What is the primary function of the GI system?
to bring nutrients into the internal environment so that they can be used
The GI tract is specialised for what four functions?
- motility
- secretion
- digestion
- absorption
What is meant by the motility function of the GI tract?
more things through the system at an appropriate rate
What is meant by the digestion function of the GI tract?
both mechanical and chemical digestion: break them into smaller pieces
Name the 6 major organs of the digestive tract
- oral cavity
- pharynx (including the oropharynx and the laryngopharynx)
- oesophagus
- stomach
- small intestine
- large intestine
Name 7 accessory organs of the digestive system
- teeth
- tongue
- salivary glands
- liver
- gallbladder
- pancreas
- anus
The structures of the gastrointestinal system are lined with __________ and are closed off at both ends by __________
epithelium
sphinctors
What are the two main epithelium in the digestive system?
- simple columnar epithelium
2. stratified squamous epithelium
What are 3 specialisations of epithelium?
- goblet cells
- microvilli
- cilia
What are microvilli and what is their function?
they are finger like extensions which increase surface area for excretion and absorption
What is the epithelium present in the mouth/oral cavity/oesophagus and how does this relate to the function of that area?
there is lots of food in this area and so to protect the inner tissue from abrasion, there is stratified squamous epithelium
What is the epithelium present in the stomach/small intestine/large intestine and how does this relate to the function of that area?
Simple columnar epithelium for secretion and absorption
What is the epithelium present in the anal canal and how does this relate to the function of that area?
stratified squamous for protection against abrasion
Epithelium can form into
glands
What is the most simple gland? Give an example
unicellular glands
eg. goblet cells
Describe goblet cells
- what cell shape are they?
- what shape are they?
- what do they secrete?
- what sort of nucleus do they have?
- columnar
- goblet shape
- mucous granules
- basal nucleus
Apart from unicellular glands, epithelium can also form ________ glands
multicellular
Epithelium can invaginate to form what two types of multicellular glands
- simple multicellular gland
- compound multicellular gland
What are simple multicellular glands?
Give two places in the GI tract where these are found
a gland with a single duct
in the stomach and small intestine
What are compound multicellular glands?
Give an example
a gland with two more ducts eg. salivary glands
What is the advantage of having many ducts in compound multicellular glands?
to increase surface area for secretion
What are the four layers of the gut tube?
- mucosa
- submucosa
- muscularis
- adventitia
What three things is the mucosa made of?
- epithelium on a basement membrane
- lamina propria
- muscularis mucosae
What is the lamina propria made of and what is in it?
it is made of fibrous connective tissue
lymphatics and blood vessels are found here
What is the muscularis mucosae and what is the consequence of it contracting?
a muscle layer of the mucosa
contraction changes the shape of the lumen and move the circular folds and villi
What two things does the submucosa contain?
glands
blood vessels
secretion from the glands is regulated by the ______ ______ ______ which is part of the _______ nervous system
submucosal nerve plexus
enteric
What does the muscularis consist of?
smooth muscle
what are the two main layers of the muscularis?
inner circular
outer longitudinal
the muscularis is under involuntary/voluntary control?
involuntary
The muscularis is under involuntary control of the _______ plexus which is part of the ________ nervous system. This is located ________ ________ _______ _______ and it regulates ________ by …
myenteric enteric in between muscle layers motility innervating the mucosa and submucosa
What is the adventitia made of? Why?
loose fibrous connective tissue for the maintenance of structure and to adhere it to the surrounding structures
When the organs are in the peritoneal cavity, they have another additional layer (as well at the adventitia) and this is called the
serosa (but this doesn’t count as one of the four layers)
What is the peritoneum?
It is a serous membrane which surrounds the organs of the GI tract
The peritoneum has two layers. What are they called and where are they located?
- parietal layer which lines the body wall
- visceral layer which lines the organs
Between the two layers of the peritoneum, there is a
fluid filled space
Where is the retroperitoneal? What is an organ that is situated here?
Posterior to the peritoneum
the pancreas
What is the mesentery?
What is its purpose?
A double layer of visceral peritoneum that connects an organ to the body wall. This is to stop the tubular portions of the GI tract to become knotted
What is the omenta?
a double layer of visceral peritoneum that connect an organ to another organ
What happens in the mouth and oral cavity?
food is ingested
What is the epithelium found in the mouth and oral cavity?
stratified squamous epithelium
What is required in the mouth and oral cavity for chemical digestion?
enzymes
Describe the flow of the bolus into the oesophagus
it travels through the fauces into the oropharynx then into the oesophagus
What are the three pairs of salivary glands connected to the oral cavity via ducts?
- parotid
- sublingual
- submandibular
What is secreted from parotid salivary glands?
serous fluid with amylase
What is secreted from sublingual salivary glands?
mucous only
What is secreted from submandibular salivary glands?
a mixture of serous fluid with amylase and mucous
What are clusters of cells in the salivary glands called?
acinus
What do acinar cells secrete?
amylase
Where are acinar cells located?
At the bottom of the duct
Where are duct cells located?
close to the secretion surface
What do duct cells secrete?
bicarbonate for buffering
Where is the oesophagus lcocated?
posterior to the trachea, extending from the pharynx to the stomach
What is the role of the epiglottis?
it shuts to ensure that the food entering the oesophagus does not enter the trachea
The oesophagus has highly folded ________ and _______ and the purpose of this is to
submucosa and mucosa
have the capacity to expand
What is the epithelium in the oesophagus?
stratified squamous epithelium
What is the role of the muscularis in the oesophagus?
to move the food bolus
How does the musclaris change as you go down the oesophagus?
- the first third is skeletal muscle
- the middle third is a mixture of skeletal muscle and smooth muscle
- the last third is smooth muscle
What is the purpose of mucous in the oesophagus?
for lubrication and protection
are there goblet cells in the oesophagus?
no, instead there are glands with ducts at the surface
If not from the goblet cells, where is mucous secreted from in the oesophagus?
from inner mucous secreting glands in the lamina propria and then shipped to the surface via ducts
